linux-ext4 - Re: [PATCH v2 19/28] mke2fs: add inline

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Message-ID: <20131204040819.GM9535@birch.djwong.org>
Date:	Tue, 3 Dec 2013 20:08:19 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
	Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH v2 19/28] mke2fs: add inline_data support in mke2fs

On Wed, Dec 04, 2013 at 11:27:57AM +0800, Zheng Liu wrote:
> On Tue, Dec 03, 2013 at 02:30:26PM -0800, Darrick J. Wong wrote:
> [...]
> > > +		 * notify users that inline data will never be useful.
> > > +		 */
> > > +		if ((fs_param.s_feature_incompat &
> > > +		     EXT4_FEATURE_INCOMPAT_INLINE_DATA) &&
> > > +		    inode_size == EXT2_GOOD_OLD_INODE_SIZE) {
> > 
> > Perhaps I'm missing something here, but why is it impossible to use i_blocks
> > for inline data even if there's no space for EAs?
> 
> If I understand correctly, on kernel side, we determine an inode has
> inline data according to whether we have 'system.data' xattr entry on
> inode extended attribute space.  If an inode doesn't have enough space
> to store an entry with 'system.data', we just think this inode doesn't
> has inline data.  So that is why I add this sanity check.

Ok.  I was curious.  Small inode => no inline data seems like an unfortunate
restriction to me, but oh well, it's your feature.  I don't plan to go back to
128 byte inodes ever. :)

Also, we could store four more bytes if we created a new e_name_index value (5?
9?) to represent "system.data".  Any thoughts about that?

--D

> 
> Regards,
>                                                 - Zheng
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